1. Field of the Invention
The present invention relates to a portable telephone set which is subject to transmission power control, and a communications system incorporating such a portable telephone set.
2. Description of the Related Art
In a communication system which employs a code division multiple access (CDMA) process for radio communications, a number of base stations and mobile stations communicate with each other in respective established links at the same frequency. The received power (desired power) of a signal in a certain link acts as interference power that disturbs other links. In an uplink transmission where a mobile station transmits a signal and a base station receives the transmitted signal, when the desired power exceeds a predetermined power level, the interference power increases, thus reducing the link capacity.
To prevent the above phenomenon from occurring, it is necessary to strictly control the transmission power of mobile stations. According to one uplink transmission power control process, the desired power from a mobile station is measured by a base station and the measured level of the desired power is compared with a control target level. If the measured level of the desired power is greater than the control target level, then the base station transmits a control command for reducing the transmission power to the mobile station. Conversely, if the measured level of the desired power is smaller than the control target level, then the base station transmits a control command for increasing the transmission power to the mobile station. The mobile station receives the control command transmitted from the base station, and controls the transmission power based on the received control command.
FIG. 1 of the accompanying drawings illustrates a process of controlling the transmission power of a mobile station based on a control signal from a base station.
As shown in FIG. 1, a mobile station 100a is positioned more closely to a base station 200 than a mobile station 100b. It is general practice to control the transmission power of the mobile station 100b so as to be greater than the transmission power of the mobile station 100a. Therefore, the mobile station 100b positioned more remotely from the base station 200 than the mobile station 100a consumes an increased current, causes a greater battery power consumption, and suffers a shorter communication time.
One solution has been to turn off a transmission power amplifier in a mobile station while no communication is made by the mobile station, for thereby preventing a current consumed by the mobile station from being increased.
A conventional portable telephone set which incorporates a scheme for achieving such a solution is illustrated in FIG. 2 of the accompanying drawings.
As shown in FIG. 2, the system comprises an antenna 101 for transmitting and receiving radio waves, a reception RF circuit 103 for spreading a radio signal received by the antenna 101 with a predetermined code, a reception baseband signal processor 104 for decoding the signal spread by the reception RF circuit 103, a reception voice signal processor 105 for converting the signal decoded by the reception baseband signal processor 104 into an analog signal, a receiver 106 for outputting the analog signal produced by the reception voice signal processor 105 as voice sounds, a transmission power processor 107 for processing a control signal for controlling transmission power which is contained in the signal decoded by the reception baseband signal processor 104, a microphone 109 for receiving and converting voice sounds into a voice signal, a transmission voice signal processor 110 for converting the voice signal from the microphone 109 into a digital signal, and controlling transmission power based on the control signal processed by the transmission power processor 107, a transmission baseband signal processor 111 for encoding the digital signal produced by the transmission voice signal processor 110, a transmission RF circuit 112 for converting the signal encoded by the transmission baseband signal processor 111 into a high-frequency signal, a PA module 113 for amplifying the power of the high-frequency signal produced by the transmission RF circuit 112 according to an amplification factor controlled by the transmission voice signal processor 110, and a transmission/reception common unit 102 for outputting the radio signal received by the antenna 101 to the reception RF circuit 103 and outputting the signal whose power has been amplified by the PA module 113 to the antenna 101. The signal whose power has been amplified by the PA module 113 and which has been outputted from the transmission/reception common unit 102 is radiated from the antenna 101.
The transmission power is amplified on the basis of the control signal processed by the transmission power processor 107. The control signal processed by the transmission power processor 107 is supplied to the transmission voice signal processor 110. Only when a voice signal is supplied from the microphone 109 to the transmission voice signal processor 110, the PA module 113 amplifies the transmission power according to the amplification factor controlled by the transmission voice signal processor 110.
In the portable telephone set shown in FIG. 2, a signal transmitted from a base station (not shown) is received by the antenna 101, and processed successively by the transmission/reception common unit 102, the reception RF circuit 103, the reception baseband signal processor 104, the reception voice signal processor 105, and the receiver 106, which outputs voice sounds. The base station also transmits a control signal for controlling the transmission power of the portable telephone set. The control signal is processed by the transmission power processor 107, and then supplied to the transmission voice signal processor 110.
A voice signal supplied from the microphone 109 is processed successively by the transmission voice signal processor 110, the transmission baseband signal processor 111, the transmission RF circuit 112, the PA module 113, and the transmission/reception common unit 102, and transmitted from the antenna 101 to the base station. The amplification factor of the PA module 113 is controlled by the transmission voice signal processor 110 based on the control signal processed by the transmission power processor 107. Only when a voice signal is supplied from the microphone 109 to the transmission voice signal processor 110, the PA module 113 amplifies the transmission power.
Even if the portable telephone set has a function to be able to turn off the transmission power amplifier when no communication is made by the mobile station, the user of the portable telephone set often fails to recognize such a function. Provided the user recognizes the function, the user tends to communicate via the portable telephone set normally without having any idea as to when and if the transmission power amplifier is turned off. Therefore, there is almost no time in which the transmission power amplifier would be turned off.
When the conventional portable telephone set is positioned remotely from the base station, the portable telephone set consumes a larger current, causes a greater battery power consumption, and suffers a shorter communication time.
It is therefore an object of the present invention to provide a portable telephone set which minimizes an increase in a current consumed thereby and has an increased communication time when the portable telephone set is positioned remotely from a base station, and a communication system which incorporates such a portable telephone set.
According to the present invention, a portable telephone set controls the amplification factor of an amplifier to control the transmission power of the portable telephone set based on a control signal transmitted from the base station. If the control signal transmitted from the base station controls the transmission power so as to be equal to or smaller than a predetermined level, then a first switching means sets the amplifier to an ON-state. If the control signal transmitted from the base station controls the transmission power so as to be greater than the predetermined level, then the first switching means sets the amplifier to an OFF-state.
While the amplifier is being set to the OFF-state by the first switching means, if the amplifier is set to the ON-state by a second switching means only when the user of the portable telephone set communicates via the portable telephone set, then the amplifier is in the ON-state only during the communication if the transmission power is controlled so as to exceed the predetermined level.
When the portable telephone set is positioned remotely from the base station, an increase in a current consumed by the portable telephone set is minimized and a communication time is prevented from being unduly shortened.
If the portable telephone set has a memory means for temporarily storing a signal to be transmitted to the base station, then when the user turns on a communication switch to initiate a press-to-talk sequence, the communication is not interrupted because the signal stored by the memory means is read and transmitted.
The above and other objects, features, and advantages of the present invention will become apparent from the following description when taken in conjunction with the accompanying drawings which illustrate a preferred embodiment of the present invention by way of example.